Steel Girder Highway Bridges Research Articles

Moment and shear estimations in steel girder highway bridges using committees of artificial neural networks and finite element models

Moment and shear estimations in steel girder highway bridges using committees of artificial neural networks and finite element models

Field-Deployable Fiber Optic Sensor System for Structural Health Monitoring of Steel Girder Highway Bridges

Structural health monitoring of highway bridges is a vital but currently challenging aspect of infrastructure engineering due to the number of sensors required, power requirements, and harsh environmental conditions. The purpose of this study is to develop a structural health monitoring system using fiber optic sensors based on fiber Bragg gratings that addresses these issues and is field deployable. Prototype systems were installed on two steel girder bridges. The first bridge used sensors adhered to the web and flange. The second bridge used a flange-only array of mechanically mounted sensors. The results demonstrated the accuracy of the fiber Bragg grating sensors and indicated that fewer multiplexed fiber optic cables and loosely routed cables were needed to maintain signal integrity. Adhered sensors were prone to lose their bond due to the curing conditions in the field. The findings suggest that the proposed system may be best used in a hybrid deployment, where a diagnostic field test with conventional sensors is used to determine the baseline bridge response and fiber optic sensors are periodically installed for short-term monitoring.

Field Load Rating and Grillage Analysis Method for Skewed Steel Girder Highway Bridges

Abstract An innovative load rating method for skewed highway bridges with steel girders is proposed in this paper. In the proposed method, a field test coupled with a grillage analysis is used to d...

Nonexplosive Deconstruction of Steel Girder Highway Bridges

AbstractWhile the transportation system of the United States rapidly ages and expands, there is increasing demand for the demolition, replacement, modification, or rehabilitation of existing bridges; all of these actions require some degree of engineered deconstruction. In a 2013 report on American infrastructure a large number of bridges surveyed were reported to be structurally deficient or functionally obsolete, and many of the existing bridges have exceeded their 50-year design life. Although highway bridges have been deconstructed around the world for generations, there are few publications on the structural engineering aspects of the deconstruction process. This paper aims to shed light on the general nonexplosive deconstruction process by presenting aspects of a three-span continuous steel girder highway bridge example. General sequence, equipment, methods, economy, and engineering are discussed. The authors also focus on the role of structural engineers, as they can be a key factor in safe and eco...

Analytical Modeling of Horizontally Curved Steel Girder Highway Bridges for Seismic Analysis

This article introduces a generic modeling approach that is suitable for static and dynamic analysis, and response assessment of highway bridges with varying levels of irregularities. The proposed approach and modeling recommendations are based on grillage modeling rules that allows explicit representation of various types of details and components. The validity and accuracy of the proposed approach is demonstrated against three-dimensional finite element models as well as experimentally recorded response various benchmark bridges. While achieving remarkable accuracy, the required analysis time was also reduced up to 80%, making the proposed approach suitable for computationally intensive studies.

Influence of skew angle on live load moments in steel girder bridges

This paper presents the results of a parametric study evaluating the effect of skew angle on the wheel load distribution in steel girder highway bridges. The finite element method was used to investigate the effect of various parameters such as the span length, girder spacing, and skew angle, on simply supported, one-span, two-lane, three-lane and four-lane steel girder bridges. A total of 270 bridge cases were analyzed and subjected to AASHTO HS20 design trucks positioned on each bridge to produce maximum bending in the interior steel girders. A combination of five typical span lengths, three girder spacing, and six skew angles were used in evaluating bending moments in skewed steel girder bridges. The finite element results were used to calculate the maximum bending moment in steel girders due to the various skew angles and compared to the reference straight bridges, and then compared to the reduction factors used in AASHTO LRFD Bridge Design Specifications. The finite element results showed the reduction in bending moment for all skewed bridges up to 30 degrees can be neglected and such bridges can be designed as straight bridges. These results are consistent with the AASHTO Standard Specifications and the LRFD procedure by not specifying any reduction factor for bridges with skew angles up to 30 degrees. For highly skewed bridges and span length less than 80 ft (24 m), the finite element results showed a reduction in moment ranging between 10% and 20% for skew angles up to 40 degrees, and between 20% and 35% for skew angle up to 50 degrees. For practical application, a conservative reduction in girder bending moment of 15% is suggested for skew angles between 30 and 40 degrees and another conservative reduction in girder bending moment of 25% for bridges with skew angles between 40 and 50 degrees. Furthermore, the AASHTO LRFD reduction factors, ranging between 15% and 5%, were more conservative when compared with the finite element results for short-span bridges with high skew angles.

Fatigue assessment of highway steel bridges in presence of seismic loading

In this study a LEFM (Linear Elastic Fracture Mechanics) approach is used in a probabilistic context to evaluate the fatigue reliability of steel girder highway bridges in the presence of seismic loading. In the first part the fatigue damage is related to the traffic load produced by heavy trucks crossing the bridge; the second part deals with the fatigue damage related to seismic loading. Both damage typologies are analyzed using linear elastic fracture mechanics principles, and the time required for an initial crack propagation is calculated. Taking into account that the correlation between fatigue effects and seismic actions is not usually considered in the literature, this method could enable a better understanding of progressive damage phenomena due to fatigue related problems, and could give some new insights for increasing the remaining fatigue life of a large number of steel bridges in seismic zones.

Full-Scale Test and Analysis of a Curved Steel-Box Girder Bridge

Since the first edition of the AASHTO Guide Specifications for Horizontally Curved Steel Girder Highway Bridges was published in 1980, there have been two more editions including many revisions to the specifications. Some changes were based on valid research results and others were based on limited or uncertain research results and information. The current edition of the specifications contains provisions that may result in unreasonably conservative load capacity ratings. In this paper, the results of field tests and analyses conducted on the Veterans’ Memorial curved steel-box girder bridge are discussed. Test and analytical results show: (1) current AASHTO guide specifications regarding the first transverse stiffener spacing at the simple end support of a curved girder may be too conservative for bridge load capacity ratings; (2) current AASHTO guide specifications may greatly overestimate the dynamic loadings of curved box girder bridges with long span lengths; and (3) a plane grid finite-element model...

Strength of Stiffened Flanges in Horizontally Curved Box Girders

Longitudinal stiffeners are often attached to increase the buckling strength of thin-walled box girder flanges. The minimum required rigidity for longitudinal stiffeners for curved box girder flanges is given by the AASHTO Guide specifications for horizontally curved steel girder highway bridges. However, this requirement is simply adopted from the current AASHTO specifications for straight stiffened flanges. The validity of this requirement has been questioned in a series of recent studies. The effect of important design parameters on the minimum required stiffener rigidity is investigated numerically in this study by examining the prebuckling stress distribution and elastic and inelastic buckling stresses of horizontally curved stiffened flanges. In order to characterize and quantify the analytically collected data, a series of parametric studies were performed. A new equation for the minimum required rigidity for the longitudinal stiffeners is derived from regression analyses. Through the evaluation of a few selected case studies and a design example, the validity and reliability of the proposed new equation is demonstrated.

Reliability validation of multigirder steel bridges designed by LRFD

The reliability index is examined for steel girder highway bridges designed by AASHTO load and resistance factor design (LRFD) Strength I limit state. The reliability analysis is based on the extensive stochastic finite element method (SFEM). The SFEM takes advantages of the conventional advanced first-order second-moment in that it considers the mechanic connection between the critical member and other members in the whole structure. The bridges are modeled as grillage beam systems. Basic design variables include sectional properties and various dead and live loads. The results obtained in noncomposite steel bridges indicate that the reliability index is very sensitive to the lateral distribution of live loads. Consequently, a simplified method is used in the reliability analysis of composite steel bridges. This simplified method can avoid the complex computation in SFEM yet achieve good accuracy. Due to overestimating the lateral distribution of live loads, the Strength I limit state in AASHTO LRFD specifications results in a conservative design for flexure but not for shear.

Dynamic Monitoring of Steel Girder Highway Bridge

Currently there are different monitoring techniques that have been considered for use in the structural evaluation of bridges. These include approaches based on both static and dynamic behavior. The use of dynamic properties has advantages over static properties, since components of the dynamic properties are only marginally influenced by variations in the loading. When dynamic properties are used, field studies have shown that it is not always sufficient to use only natural frequencies and modal displacements. Some research for structural evaluation of bridges indicates that techniques based on use of derivatives of the natural frequencies and the modal displacements may be more effectively used to generate effective diagnostic parameters for structural identification. This paper presents the results of applying one of these methods, the modal flexibility approach, to a field study of a bridge in which the bearings were partially restrained in colder weather. While others have used impact methods with the modal flexibility method, in this study the approach is modified so that excitation is provided by vehicular traffic. The results show that the modified modal flexibility method provides a clear indication that there have been changes in the bridge's structural behavior.

Nonlinear Analysis of Composite Steel Girder Bridges

This paper describes a procedure for the nonlinear analysis of composite steel girder highway bridges. The procedure uses a modified grillage (grid) analysis method where material nonlinearity is modeled by empirically derived moment-curvature relationships. These are obtained from experimental data on the behavior of typical composite steel girder bridges. A linear variation of plastic curvature along the length of each beam element is assumed. An equivalent grid plastic hinge length is used to simulate the extent of plastification over the whole length of a grid element. The procedure can account for span continuity by including a negative bending moment curvature relationship. Numerical investigations verify the proposed method's validity by comparing the analytical results with those of in-situ and laboratory full-scale and model-scale bridge tests. This paper also demonstrates that the proposed nonlinear analysis method provides a simple tool that can be used to obtain reasonably accurate representations of the nonlinear behavior of composite steel girder bridges. The method uses a grillage discretization technique whose results are relatively insensitive to variations in the mesh size. The proposed method has a high potential for use in engineering practice because of the simple input requirements and its reasonable level of accuracy.

Optimal Life-Cycle Costing with Partial Observability

Optimal costing of structures requires taking into account lifetime management (inspection and maintenance) costs in addition to initial construction cost. Recently published papers on lifetime costing have used Markov decision process models to incorporate management policies into structural reliability analysis. In this paper, an optimization model is described based on partially observable Markov decision processes. The model depicts varying levels of uncertainty inherent in differing inspection techniques. The costs and inherent uncertainties of these techniques are related to environmental degradation from fatigue and corrosion processes. The mathematical approach leads to a management policy that explicitly includes frequency and type of inspection and extent of repair. The model is demonstrated in an example involving the management of a steel girder highway bridge.

Finite-Element Analysis of Steel Girder Highway Bridges

This paper compares the performance of four finite-element modeling techniques reported in the literature used in evaluating the wheel load distribution factors of steel girder bridges. A typical one-span, simply supported, two-lane, composite bridge superstructure was selected for this study. American Association of State Highway and Transportation Officials (AASHTO) HS20-44 design truck loads were positioned to produce maximum moments in the girder. Two finite-element programs, SAP90 and ICES-STRUDL, were used to perform the analysis along with their preand postprocessing capabilities. The results of these modeling techniques were compared with AASHTO wheel load distribution factors (in 1996 and in 1994) and published experimental results. The four finite-element modeling techniques yielded similar load distribution factors. Further parametric study, varying the span length and girder spacing, was conducted and the distribution factors obtained using two of the four finite-element modeling techniques co...

Vulnerability Assessment Of Large StructuresSubjected To Damage From Dynamic Loading

This paper describes the development of a new approach to vulnerability assessment based upon the use of engineering analysis. The effects of the transient dynamic loading from the event in causing local damage to structural elements are considered and the residual resistance of the damaged structure is assessed. The use of dynamic finite element analyses to predict local damage from these events is discussed in the companion paper by Wright and Hobbs. Structural analysis using the residual strength parameters is then used to predict the extent of any resulting structural collapse. An Index of Vulnerability is developed to categorise structures in relation to their vulnerability to different causes of local damage. The use of the approach is demonstrated for two typical large steel girder highway bridges. A range of forms of local damage at different positions on the bridge is considered and results are presented in terms of the likely modes of structural collapse and graphical presentation of the vulnerability index. The important influences of the exact structural details and the support conditions of the structure are highlighted.